Just like the apparent "duplicate message" issue, this began the very day (I checked) that we switched to using OAuth for outbound email. What I really don't understand is that this is an issue with INBOUND messages. Basically, where Inbox messages used to be moved to Delete Items after processing into tickets, they're now (effectively) being "secure" deleted from the mail account. Now, the only messages that end up in Deleted Items are REJECTED messages. However, all PROCESSED messages are nowhere to be found. Then in Ticket History, the header information is being stripped from the downloadable messages.
We often have to download and forward the original emails to another department who aren't using the ticket system. However, now we have no emails in the account and no header info in the message files saved in WHD. Did I miss something in the release notes? Is there a setting I'm not finding? And why would this start only when updating the OUTGOING mail protocol???